In March of 2009, NIH announced the availability of Recovery Act funds for competitive revision applications (NOT-OD-09-058). In response to that announcement, this application seeks to expand the scope of a project that is directed at understanding the role of nuclear Abl tyrosine kinase in DNA damage-induced cell death response. DNA damage inducers, i.e., genotoxins, are some of the most effective agents in cancer therapy. Therefore, fundamental understanding of genotoxin-induced cell death mechanisms holds the promise of enhancing the efficacy of cancer therapeutics. Studies from our laboratory have identified the nuclear Abl tyrosine kinase as an activator of cell death response to DNA damage. We have recently found that activation of Abl tyrosine kinase can regulate the expression of microRNAs. MicroRNAs are non-coding RNAs that are between 18~25 nucleotides in length. The human genome contains 500 to 600 miRNA genes, the expression of which is regulated during embryonic development, cellular differentiation and in response to genotoxic stress. Three miRNA genes are targets of regulation by the p53 tumor suppressor and they contribute to DNA damage-induced cell death. However, little is known of the mechanisms by which DNA damage regulates the expression of other miRNAs. The proposed study will fill this knowledge gap by pursuing the miRNA regulatory function of nuclear Abl. With the two-year funding from the Recovery Act, we will investigate the hypothesis that Abl phosphorylates the RNA polymerase II-CTD to recruit a nuclear Drosha-complex to stimulate the expression of specific miRNAs. We will (1) investigate the interactions of Abl, tyrosine phosphorylated RNA polymerase II and the Drosha-complex with the identified miRNA genes and their pri-miRNA transcripts and (2) determine the role of Abl-regulated miRNAs in DNA damage-induced cell death by focusing on the Eya1 and Eya3 transcription factors, as their miRNAs are predicted targets of an Abl-regulated miRNA, and they have recently been shown to antagonize the cell death response to DNA damage through their tyrosine phosphatase activity. The proposed research will investigate a previously unknown pathway that transduces DNA damage signals to the regulation of miRNA expression and cell death. Because Abl is not mutated in sporadic human cancers and because Abl can activate p53-independent cell death, results from the proposed research will shed light on how to exploit the pro-apoptotic miRNAs induced by DNA damage through Abl to kill tumor cells. PUBLIC HEALTH RELENVANCE: The proposed research will acquire fundamental knowledge on how DNA damage triggers cell death. In particular, this research will investigate a previously unknown effect of DNA damage inducing agents, e.g., ionizing radiation, cisplatin and doxorubicin, on the expression of microRNAs, which are non-coding RNAs that regulate the functions of protein-coding mRNAs. Results from this study will advance our understanding of cellular response to DNA damage and this knowledge will help to reduce the harmful side effects while improving the efficacy of cancer therapy.